Surveillance cameras are widely used as an aid in providing physical security for employees and property, for example in commercial, industrial and government facilities. In many instances, the images from a camera are simply viewed in real time by security guards at a central location.
It is also common to record the output of each camera using some suitable storage device, such as a video cassette record (VCR). In the event of a problem or security incident, the saved video information can then be examined. However, video surveillance applications can generate thousands of hours of video information, and a large amount of storage capacity is needed to save all of this video information. Similarly, a large bandwith is needed in order to transmit all of this video information to a remote location. There are some existing techniques which can be used to reduce the amount of information which must be saved or transmitted.
One approach is to use temporal sampling, such as time-lapse video recording. In essence, some of the detected video images are simply discarded, in order to reduce the overall amount of information which must be stored. As one example, every tenth or twentieth image would be selected for storage, and all other images would be discarded. This approach does have the advantage of reducing the amount of information which must be saved. However, a disadvantage is that the saved information is not sufficiently complete to allow accurate automated object tracking using known motion segmentation techniques.
A different approach involves spatial sampling, in order to reduce the resolution of the image information which is saved. For example, every detected image may be subsampled, in order to significantly reduce the total number of pixels for that image. By saving each image in a reduced resolution format, the total amount of image information which must be saved is reduced. A disadvantage is that the spatial resolution is uniformly low in each image, and thus throughout the video sequence.
A third approach involves the use of known video compression techniques. One known technique involves saving a full image, and thereafter saving only the portions of subsequent images which differ from the full image. However, in a real-time application, special purpose compression hardware and/or temporal and spatial sampling may be required, in order for the system to be able to compress video information at least as fast as it is being generated. Special purpose hardware may also be required to decompress the image information, if the decompressed image information must be provided on a real-time basis.
Thus, although each of these known approaches has been generally adequate for its intended purposes, each has at least one associated disadvantage. Consequently, these known approaches have not been satisfactory in all respects.